Breathe easy – you can’t actually gain weight from just one double cheeseburger, nacho fries, and a chocolate milkshake kind of meal. So nix the guilt, enjoy your indulgence, and resume a healthy diet the next morning, says Kelly R. Jones M.S., R.D., C.S.S.D., L.D.N. “With 3,500 calories in a pound, it would take a very unhealthy binge to gain real weight in one sitting,” she says.

But, still, that doesn’t mean a night of junk doesn’t affect your body in other ways.

What Qualifies As A Pig-Out?

You’re probably wondering exactly how many calories it takes before a treat turns into an all-out nosh fest. We all have individual calorie requirements, but it’s safe to say that eating 1,000 calories in one sitting qualifies as a pig out, says Maggie Moon, M.S., R.D.N., author of The MIND Diet.

And it’s easier to get there than you might think. A big drive-thru burger with a medium fries and soda comes in close to 1,100 calories, while even salads at some chain restaurants break that 1,000-calorie mark, says Moon. Yep, we’ve definitely done it more than a handful of times.

And then there’s the heartburn. “The stomach secretes hydrochloric acid to begin the digestive process and to kill as much bacteria as it can before the food moves on through the digestive system,” Jones says. The more food you eat the more acid you produce, and some of that extra acid can find its way back up the esophagus and cause discomfort, she says.

As your body calls all-hands-on-deck to digest your junk, it sends more blood to your GI tract, which means less blood is available to transport oxygen and nutrients to other parts of your body, Moon says. This can leave you feeling sluggish and maybe even light-headed, she says.

And, beyond the stomach upset, an all-out eat fest will spike your blood sugar, especially if your food was high in carbs or sugar, giving you a quick energy boost. When your blood sugar rises like this, you release the hormone insulin, which ensures the nutrients you’ve consumed are taken up by our cells to be used, Moon says. But when you overeat, you release too much insulin, which signals to your body that you don’t need all of the energy as fuel and so you store some as fat. And as quickly as that blood sugar rises, it crashes, making you feel like a sloth.

This barrage of discomfort often leads to a crummy night of sleep, especially if you have acid reflux. “Lying down after eating a big meal can really exacerbate your discomfort,” she says. And the aftermath of that poor sleep can throw off your entire next day.

All the insulin that your pancreas churned out the night before can actually set off hunger cues and eventually make you feel even hungrier than you were before. “This can obviously lead to overeating,” Moon explains. And when your blood sugar dips too low after spiking, you may experiences headaches, difficulty concentrating, fatigue, and brain fog, because your body needs glucose (a.k.a. sugar) to fuel itself, she says.

Finally, while that one trip through the drive-thru won’t make you actually gain a pound of fat, it will lead a couple pounds of bloating and water retention, says Moon. So when you step on the scale the next morning and notice it ticks upwards, it’s because your body is holding onto water after taking in excess fats, salt, and sugar. Basically, when there’s too much sodium in your system, for example, your body retains water to dilute its concentration, she says.

What Are The Long-Term Effects?

An occasional Saturday night pizza run with friends won’t do much damage, but if pig-outs become a habit, you may be in for some pretty gnarly side effects.

Like, yes, stretching your stomach. “The average stomach is about the size of a fist and can hold less than a cup when empty, but it can expand about five times that size to hold more than four cups of food and drink,” says Moon. YIKES. Pigging out too often and stretching out your stomach can actually disrupt your hunger and stopping-point cues, which can lead to a cycle of overeating, she says.

Plus, when you chronically spike your blood sugar levels, you promote fat storage, says Jones. This weight gain may increases your risk for developing type 2 diabetes, Moon adds. Basically, when you put too much demand on your pancreas to churn out insulin over and over again, it struggles, leading to higher blood sugar a condition known as insulin resistance, she explains.

Going too hard on the junk food too often can also change the bacteria in the gut, which can lead to worsened digestion over time, Moon explains. Whole foods especially plant foods that contain fiber are the ideal food for the good bacteria in your gut, she says. That pint of ice cream or cheese-steak? Not so much.

Perhaps most scarily, eating super large meals at night can increase your risk of obesity and heart disease, says Moon. (Sad but true: A recent review published in Nutrients supports backs this up.)

Get Back To Business

When your eat fest is over, the best thing you can do is move on. Moon recommends doing 15 minutes of light exercise, whether it’s a walk or light housework, and sipping on water, which can move digestion along after you’ve let your belly settle enough to get moving.

Also, stay away from booze, which can further delay digestion and make you hungrier, she adds. Spend the next few days loading up on high-fiber foods (like fruits and vegetables) and water to nourish your body, keep your digestive tract chugging along, and flush out your system, Moon says. As long as you get your healthy eating back on track, any water weight you gained after noshing should disappear, says Jones.

Keep in mind that while some people might recover in 24 hours, others might need up to three days to get rid of the sugar, salt, and carb bloat, says Jones. Sticking to clean eats and being mindful of your body and how it responds will help you bounce back from your pig-out and keep you from going overboard in the future.